let screenWidth = window.screen.width;
//x轴出现的位置个数
// let a = parseInt(Math.random() * screenWidth / 100) * 100
//z轴范围0-1000px，步长100px，每个div span个数
let numYZSpan = [
    [0, 0,24],
    [-310, -1000,35],
    [-280, -900,33],
    [-250, -800,32],
    [-218, -700,30],
    [-187, -600,28],
    [-157, -500,27],
    [-123, -400,26],
    [-93, -300,25],
    [-61, -200,24],
    [-30, -100,23]
];